Request for advice regarding the manufacture of a spring anchor (GIF image included)

[John2006]

Hi everyone,

I just joined the forum today and this looks like a fantastic forum. I would like to say thanks to the people that created and run the forum.

I have uploaded a small 19KB .GIF file to rapidshare (and also attached) showing a drawing of a simple adjustable spring anchor I am making from a 10-32 screw. Here is the download link...

http://rapidshare.de/files/24739574/...Screw.gif.html

Regarding the drawing, an extension spring hook goes through the .098" hole, and the other end of the screw gets a hex nut that can be no larger than 5/16" flat to flat, such as part # 90760A411 from www.mcmaster.com. Due to space limitations, the hex nut must be adjusted with a box end wrench.

The .359" to .390" OD spring ( similar to the #80583 www.centuryspring.com) uses .08" diameter wire, but the problem I ran into is that the hole is not really large enough for the spring, due to the curvature of the hook.

Can a machinist cost effectively just make a .098" wide slot in the screw, about .145" to .155" long, instead of a .098" hole?

I know slots are generally easy to do, but since it is so small, I wanted to get some feedback. If the slot can be made cost effectively, It will work well with the spring. I just don't want to change the design, send the dwg off for quotes, and then have the machinist tell me it can't be done or is too expensive for the product. I need to keep things cost effective.

I suspect a small end mill may work, if breakage can be kept to reasonable levels.

If the slot cannot be made cost effectively, then I must use a larger screw that will allow for a hole of about .145" OD. A 1/4-20 or 1/4-28 screw would work great, but I could not find a nut that is 5/16" flat to flat max, and that has a 1/4-20 or 1/4-28 thread.

I did find a 1/4-32 nut (part # 91862A516) from www.mcmaster.com, which is only 5/16" flat to flat, but then I can't seem to find a screw for it. Mcmaster also sells a 1/4-40 nut that would work, but same problem, I cannot find a screw.

I would appreciate any feedback anyone can provide. Hopefully, just creating a slot in the 10-32 screw is viable and cost effective.

Thanks for your help.
John

[John2006]

Hi everyone,

Ned Simmons from another forum just pointed out that it may be cheaper to machine a flat on the screw, like a standard spring hook shown on page 3114 of the Mcmaster catalog www.mcmaster.com. For example, see image of Mcmaster part # 9634k13. This should allow the screw anchor to clear the hook curvature of the spring.

If I do this, the flat will only be about .0625" thick in order to clear the spring hook. The spring will only have about 40 to 50 pounds on it so as long as a thin flat like that can be machined without problems, it may be a viable option.

Which would be cheaper, machining a slot, or milling a flat like a standard spring anchor and then drilling the hole ?

Thanks again guys,
John

[2muchstuff]

40 to 50 pounds seems like a lot of force to pulling sideways on a #10 bolt.

[John2006]

Hi 2muchstuff,

Thanks for your reply.

Actually, if you look at the stock spring anchors from mcmaster carr, their 8-32 screws are rated for 170 pounds and the 1/4-20 is rated for 500 pounds. A 10-32 will be somewhere inbetween. I think I will be fine as far as force is concerned.

John